1. Field of the Invention
The present invention relates to a clock generation apparatus and method. More particularly, the invention relates to an apparatus and method adjusting the frequency of a reference clock adapted for use in a hard disk drive.
This application claims the benefit of Korean Patent Application No. 10-2006-0069268, filed on Jul. 24, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
2. Description of the Related Art
Hard disk drives (HDDs) have been used for many years as convenient and economical data storage devices. In general, an HDD records data on a disk and subsequently reproduces the data using one or more magnetic head(s). Current design and manufacturing trends often seek to miniaturize HDDs while maintaining (or increasing) data storage capacity. Such trends lead to smaller HDDs characterized by higher data storage capacity and greater data recording density. Greater data density results in an increased number of bits per inch (BPI) being recorded on ever more densely packed data tracks on a disk, (i.e., both radial and track-linear recording densities are increased). Such changes, however, require very fine positioning control for the magnetic head relative to the very densely recorded data in contemporary HDDs.
Conventional HDDs perform read and write operations by determining the position of a data sector in relation to servo information obtained at a constant time interval from the rotating disk. This data sector data is read by at a constant speed by a transducer. In an ideal case, a constant number of clock pulses will be generated by constituent HDD circuitry regardless of the specific sector data being read.
Unfortunately, the ideal case is seldom realized. Various eccentricities, external vibrations, and non-uniformity in the recorded servo sector intervals generated during the servo data write process result in a variable clock frequency being obtained from different data sectors. That is, the time interval of certain clock pulses generated in relation to sector data is different for different data sectors. This result adversely affects servo control and magnetic head positioning within the HDD and the reliability of write/read operations suffers accordingly.
This problem has been previously recognized. Indeed, embodiments of the invention may be better understood in a background context provided by Korean Patent Application No. 10-2005-0112779 and U.S. Pat. No. 5,724,204, the collective subject matter of which is hereby incorporated by reference. For example, Korean Patent Application No. 10-2005-0112779 discloses one technique for correcting the timing of a servo gate pulse according to a spindle jitter value, where spindle jitter is detected in a disk drive. U.S. Pat. No. 5,724,204 discloses one technique for preventing a sync signal detection error due to a detected defect in the disk.